1. Selection bias!

We can detect extrasolar planets only when they are either large/massive and/or when they are close to their parent stars.

So we discover lots of big planets in close orbits. And, of course, the first small planets will also be close in. It's like the drunk who drops his car keys and looks for them under the street light because he can see them better.

I suspect that Earth-sized planets are plentiful in the universe. All star systems have at least one. (Ours has two!) I also suspect that life is plentiful -- it's going to be everywhere.

Why do I think that? Because we know that the same rules of the universe operate here on Earth that operate at the greatest distances in the universe that we have data. Okay! Dark Energy was a surprise, but there's no reason why it cannot also be part of the universal model. Dark Matter goes back about 80 years, so it isn't exactly new.

But, life is undoubtedly plentiful, it's just that the distance to even the closest stars is so great, that travel is very impractical and costly (not just financially).

That's why we have no alien visitors, no matter what the kooks in Roswell, NM think.